XML in a Nutshell, 3rd Edition

Points

XPaths, shorthand pointers, and child sequences can only point to entire nodes or sets of nodes. However, sometimes you want to point to something that isn’t a node, such as the third word of the second paragraph or the year in a date attribute that looks like date="01/03/1950“. XPointer adds points and ranges to the XPath data model to make this possible. A point is the position preceding or following any tag, comment, processing instruction, or character in the #PCDATA. Points can also be positions inside comments, processing instructions, or attribute values. Points cannot be located inside an entity reference, although they can be located inside the entity’s replacement text. A range is the span of parsed character data between two points. Nodes, points, and ranges are collectively called locations ; a set that may contain nodes, points, and ranges is called a location set . In other words, a location is a generalization of the XPath node that includes points and ranges, as well as elements, attributes, namespaces, text nodes, comments, processing instructions, and the root node.

A point is identified by its container node and a non-negative index into that node. If the node contains child nodes—that is, if it’s a document or element node—then there are points before and after each of its children (except at the ends, where the point after one child node will also be the point before the next child node). If the node does not contain child nodes—that is, if it’s a comment, ...